Column ovens have been used in various kinds of chromatographic apparatus such as gas chromatographic apparatus and liquid chromatographic apparatus. A column oven controls the temperature of any columns so that a component to be analyzed or to be preparatively isolated is properly separated. Because the temperature of a column has a great influence on the ability of a packing material to absorb and desorb each major component, high-precision temperature control is required for achieving efficient component separation as well as excellent reproducibilty.
For this reason, a column oven with a double chamber structure (Patent Literatures 1 and 2) or a preheating technique before introducing the outer air into a constant-temperature bath (Patent Literature 3) has been used.
Particularly, a liquid chromatographic apparatus using a mixed solvent and a differential refractometer utilizes a plurality of columns for sample and reference analysis, where the temperature of an effluent from the columns affects the refractive index. Thus, a small temperature change in each column or a temperature difference between the columns affects the stability of a baseline as a noise, and the baseline tends to be destabilized.
Conventional column ovens have not been able to achieve sufficient temperature stability and they have had difficulties in making the maximum use of the abilities of the latest high-sensitivity detectors.
In this regard, as a result of verification with use of a liquid chromatographic apparatus having a differential refractometer, the inventors herein found that key factors affecting destabilization are: on/off operation of a heater, the temperature distribution within an oven, and the ambient temperature change around an oven. Particularly, the temperature distribution in a column chamber is greatly affected by any temperature change and temperature distribution outside the column chamber, even by 0.1° C. increment or decrement.    Patent Literature 1: Japanese Unexamined Patent Application Publication H5-87793.    Patent Literature 2: Japanese Unexamined Patent Application Publication 2005-140505.    Patent Literature 3: Japanese Unexamined Patent Application Publication 2001-13126.